Power over Ethernet (PoE) allows a powered device (PD) such as an Internet Protocol (IP) telephone, a wireless LAN Access Point, and a Security network camera to receive power, along with data, over an Ethernet cable. In a PoE network, a power sourcing equipment (PSE) can be connected to one or more powered devices (PDs) through an Ethernet cable. The PSE can allocate power to the one or more PDs and apply the power to the one or more PDs over the Ethernet cable. An Ethernet cable can include four pairs of wires, with each pair of wires being a twisted pair that is utilized for differential signaling. In some PoE networks, only two of the four pairs of wires in the Ethernet cable are utilized for applying power to the one or more PDs. However, it has become increasingly common for all four pairs of wires in the Ethernet cable to be utilized for applying power to the one or more PDs. By utilizing more than two pairs of wires, the PoE networks can support higher current with reduced cable loss.
In allocating power to one or more PDs in a PoE network, a PSE can determine power loss and budget power allocation amongst the one or more PDs accordingly. Due to imprecise determination of power loss, the PSE may, for example, estimate power loss and, based on the estimated power loss, cease applying power to one or more of the PDs in order to maintain a desired power efficiency in the PoE network. As another example, the PSE may imprecisely allocate less power to one or more of the PDs based on a worst-case scenario. In PoE networks, Ethernet cable resistance is a large contributor to power loss. As such, the PSE would estimate Ethernet cable resistance to determine power loss. For example, time domain reflectometry could be utilized along with average resistance per unit length of an Ethernet cable to estimate Ethernet cable resistance.